* If you stop your client/server, your data must be distributed 3rd party nodes, that are owned by onknown people, so you don't get 100% guarantee your data is available if you close your client. * You won't be able to use this social network if you only have a browser, or if everything except HTTP traffic is blocked. * Add the usual about network effects, about how noone will switch because all their friends are already on facebook, etc. Also, NAT and piercing NATs is still an issue, especially if you are running something like this on your mobile.
If the servers are set us as bittorrent nodes, or something similar, with redundancy built in, that should address the issues you raise.